[time-nuts] Got 60HZ?

[paul swed]

WHAT chip are you using that has the nice divide by 10 outputs please?
I have been wiring 74ls XXXs for years what a pain. Tired of the soldering.
Thanks
Paul

On Thu, Dec 9, 2010 at 7:47 AM, Bob Camp <lists at rtty.us> wrote:

> Hi
>
> Another simple approach:
>
> Run a PIC off of it's internal R/C clock
> Divide to both 60 Hz with a divider that will do M, M-N, M+N where N is
> 1,2,3,4,5 and covers the expected tolerance of the clock
> Divide the 60 Hz to 1 Hz
> Compare the 1 Hz to a pps output
> Based on the 1 Hz being early / late, update N for the next second.
>
> It actually takes less time to code it than to explain it like this.
>
> If the built in clock is good to ~ 0.1 % on a second to second basis, your
> clock will be far more accurate than the eye can detect.
>
> Lots of ways to do it.
>
> Bob
>
>
> On Dec 9, 2010, at 3:47 AM, francesco messineo wrote:
>
> > Hello,
> >
> > On Thu, Dec 9, 2010 at 5:13 AM, Michael Poulos <poulosmd at gmail.com>
> wrote:
> >> Recently I bought a Efratom Ru frequency standard from eBay and a
> frequency
> >> divider chip that makes 1MHZ,100KHZ,25KHZ,10KHZ,100HZ and a 1HZ output.
> >> Today I thought of a way to make a nice 60HZ so you can use a
> mains-powered
> >> clock for the display (using amplifier and transformer wired
> "backwards").
> >> But, now you'll need 60HZ. A European has it easy with 50HZ as you use a
> >> BASIC Stamp or Arduino to divide the 100HZ output. But for 60HZ I came
> up
> >> with a solution:
> >>
> >> You set up the Arduino to take the 10KHZ from the divider chip and
> program
> >> it to count off 83 pulses to flip an output. But wait! Unless you add a
> >> "leap count" every 3 flips of the output, it'll run fast. Assume at the
> >> start the Arduino output starts high then turns low:
> >>
> >> (83+83+84+83+83+84)*20 = 10,000 pulses = one second
> >> H__L__H__L__H__L
> >>
> >> Every output cycle and a half the voltage swing is a little over 1
> percent
> >> longer because of the leap count. This means that the distortion adds a
> >> slight inaccuracy, not enough to upset New Year's revelers. But if you
> want
> >> a better 60HZ, try using the 100KHZ:
> >>
> >> (833+833+834+833+833+834)*20 = one second
> >>
> >> You see where this is going with leap counts. The ultimate of course is
> one
> >> really good Arduino and (after a hex inverter to amplify it) take the
> >> straight 10MHZ and apply this leap count technique:
> >>
> >> (83333+83333+83334+83333+83333+83334)*20 = one really accurately made
> 60HZ =
> >> one nice second, just the thing for a Nixie clock. :)
> >>
> >> Now, what is a good hex inverter to take the 10 million HZ of my
> rubidiom
> >> movement to feed a frequency divider chip (and later Arduino)? It needs
> to
> >> take the .5 of a volt sinewaIe and squarewave it and in a normal 14 pin
> DIP
> >> (breadboardable) package.
> >
> >
> > if you are not afraid of a little microcontroller programming, why not
> > use a software DDS approach like this:
> >
> >
> > http://www.myplace.nu/avr/minidds/index.htm
> >
> > it can output a nice sine wave at 60 Hz (or whatever) from say a 10
> > MHz clock really easily and the frequency is also easily tunable in
> > software.
> >
> > I built several similar low frequency (audio range) software DDS using
> > AVR and other microcontrollers.
> > I usually add a one or two stage active low pass filter after the R/2R
> > network. I also used to build the R/2R network out of selected 1% 10K
> > resistors, final resistor match is usually good to 0.1% tolerance, but
> > in some boards I just put 5% parts.
> > Software is basicly an adder and you use the highest byte as a pointer
> > to the ram or rom waveform samples, once you understand how it works,
> > it's really easy to adapt to your needs. Usually the waveform you
> > obtain has a DC offset, but that's easily solved too.
> >
> > Hope it helps.
> >
> > Frank   IZ8DWF
> >
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